Conventionally, the position estimating system utilizing radio communication has been employed as a system for employing a radio transmitter and a radio receiver to estimate a position of an object.
In Patent document 1, Patent document 2, Patent document 3, and Patent document 4 the technology is disclosed of installing a radio receiver in a location of which the position is known, receiving an inherent ID being transmitted from a radio transmitter, with which the object has been equipped, with the radio receiver, and estimating a position of the object by making a reference to the location of the radio receiver. In Patent document 5 and Patent document 6, the technology is disclosed of installing a radio transmitter transmitting an inherent ID in a location of which the position is known, specifying the radio transmitter from the inherent ID received by the radio receiver with which the object has been equipped, and estimating a position of the object by making a reference to the location of the specified radio transmitter. In Patent document 7 and Patent document 8, the technology is disclosed of measuring a radio wave intensity at the moment of receiving an inherent ID being transmitted from the radio transmitter with the radio receiver, and estimating a distance between the radio transmitter and the radio receiver or comparing a radio wave intensity thereof with a pre-acquired radio wave intensity pattern, thereby to estimate a position of the object equipped with the radio transmitter or the radio receiver. In Patent document 9, the technology is disclosed of measuring an arrival time of a signal at the moment of receiving an inherent ID being transmitted from the radio transmitter with the radio receiver, thereby to estimate a distance between the radio transmitter and the radio receiver and to estimate a position of the object equipped with the radio transmitter or the radio receiver.
Further, in a radar system of Patent document 10 and Patent document 11, a distance to the object is estimated by measuring the time that elapses from reflection of the radio wave transmitted from the radio transmitter installed in a location of which the position is known upon the object to reception of the radio wave by the radio receiver installed in a location of which the position is known, and a position of the object is estimated by making a reference to the location of the radio transmitter.    Patent document 1: JP-P2001-092885A    Patent document 2: JP-3336300B    Patent document 3: JP-P2005-055186A    Patent document 4: JP-P2004-046904A    Patent document 5: JP-P2004-297334A    Patent document 6: JP-P2004-251816A    Patent document 7: JP-P2004-294403A    Patent document 8: JP-P2004-112482A    Patent document 9: JP-P2003-078947A    Patent document 10: JP-P1997-236651A    Patent document 11: JP-2679360B